Method and device for flow reconstruction

ABSTRACT

The invention relates to a method and a device for the three-dimensional reconstruction of the flow conditions in a vascular system ( 3 ), in which, in a first phase after the beginning of a contrast-medium injection, X-ray projection pictures are produced from the same direction (A) at a high picture-taking rate in order to observe the inflow of the contrast medium. When the contrast medium fills the vascular system ( 3 ), a rotation of the Xray device ( 1 ) takes place during which projection pictures are produced at a lower picturetaking rate and/or at a lower radiation dose, from which pictures the three-dimensional structure of the vascular tree can be reconstructed. Optionally, at the end of the rotation, projection pictures may again be taken from a fixed direction that observe the drainage of the contrast medium from the vascular system ( 3 ).

The invention relates to a method and a device for the three-dimensionalreconstruction of the flow conditions in a vascular system with the aidof two-dimensional projections of the vascular system during acontrast-medium injection.

To assess diseases of the vascular system, it is desirable to know theflow conditions prevailing therein in conjunction with athree-dimensional model of the vascular tree. In this connection, it isknown, for example, from U.S. Pat. No. 4,577,222 to inject contrastmediums into a vascular system and to track the spreading of thecontrast medium with the aid of a series of projection pictures.Furthermore, it is known from three-dimensional X-ray rotationangiography (“3D-RA”) to reconstruct a three-dimensional vascular treefrom two-dimensional projection pictures of the vascular tree taken fromdifferent directions. In the production of such angiograms, a contrastmedium is also as a rule injected so that the vascular tree to berecorded is displayed as well as possible on the X-ray pictures.

Against this background, it was the object of the present invention toprovide means for the three-dimensional reconstruction of the flowconditions in a vascular system, which means entail as little exposureas possible for the patient.

This object is achieved by a device having the features of claim 1 andalso by a method having the features of claim 7. Advantageousrefinements are contained in the subclaims.

The device according to the invention serves for the three-dimensionalreconstruction of the flow conditions in a vascular system with the aidof two-dimensional projections of the vascular system during acontrast-medium injection. “Contrast medium” is to be understood in thisregard in a wide sense as meaning any medium or object whose movement ina vascular system is observable and during this process makes possibleconclusions relating to the flow conditions in the vascular system. Thedevice comprises the following components:

-   An imaging device for producing two-dimensional projection pictures    of the vascular system taken from different directions. Said device    may be, in particular, a rotation X-ray unit, such as is known, for    example, from computer tomography.-   An injection device for the controlled injection of a contrast    medium into the vascular system. As a rule, such an injection device    will comprise an injection pump and a catheter, the catheter being    pushed forward via an access to the vascular system up to an    examination point of interest (for example, the heart).-   A control unit that is coupled to the imaging device and that is    designed to drive the imaging device in accordance with the    following steps:

a) First step: production of projection pictures of the vascular systemtaken from the same projection direction during the inflow of thecontrast medium, that is to say from the beginning of a contrast-mediuminjection. The chosen picture-taking rate is to be high in this case sothat the spreading of the contrast medium in the vascular system isrecorded with good time resolution in the projection pictures.

b) Second step: Rotation of the imaging device around the vascularsystem to produce projection pictures taken from different directionswhile the contrast medium injected in the first step fills the vascularsystem. The projection pictures produced in this way show the entirevascular system in an optimum way so that the three-dimensional vasculartree can be reconstructed from said pictures. The methods known fromrotation angiography, which, inter alia, may comprise a selection ofprojection pictures from the same ECG or heartbeat phase may, inparticular, be used for the reconstruction.

The device described makes it possible to record both the spreading ofthe contrast medium and consequently the flow conditions with a singlecontrast-medium injection, as well as to reconstruct the vascular treethree-dimensionally. The stressing of the patient by the contrast mediumis consequently kept to a minimum level.

In particular, if the imaging device is an X-ray unit, the control unitis furthermore optionally designed to effect production of projectionpictures at a lower picture-taking rate and/or at a lower radiation doseduring the rotation of the imaging device. The lower radiation dose canbe brought about in the case of an X-ray unit, for example, by asuitable adjustment of the tube current and/or the tube voltage.Reducing the picture-taking rate and/or the radiation dose ensures thatthe radiation exposure of the patient is limited to a minimum while therotation pictures are taken.

In accordance with a further aspect of the device, the control unit isfurthermore designed to drive the imaging device after completion of therotation in such a way that it produces further projection picturestaken from a constant projection direction. Preferably, this productiontakes place again at a high picture-taking rate. Such pictures at theend of the rotation make it possible also to observe the draining of thecontrast medium from the vascular system in a time-resolved manner.

In accordance with another aspect of the device, the control unit isdesigned to initiate the beginning of the rotation of the imaging deviceas a function of an image analysis of the projection pictures takenduring the inflow of the contrast medium. In particular, it is possibleto determine from the projection pictures produced during the inflow theinstant in time at which the contrast medium fills the entire vasculartree, i.e. the inflow process is complete and the conditions exist forthe rotation pictures.

Furthermore, the control unit may also be coupled to the injectiondevice for the contrast medium in order to record and/or to control theinjection process automatically. During a recording of the injectionprocess, the control unit can, for example, obtain information aboutwhen a user initiates a contrast-medium injection so that the controlunit can effect the production of projection pictures in harmonytherewith. If the control unit can control the injection device, it caninitiate the injection operation automatically itself.

The invention furthermore relates to a method for the three-dimensionalreconstruction of the flow conditions in a vascular system with the aidof two-dimensional projection pictures of the vascular system takenduring a contrast-medium injection that comprises the following steps:

a) Production of projection pictures taken from the same projectiondirection with a high picture-taking rate during the inflow of thecontrast medium;

b) Production of projection pictures of the vascular system taken fromdifferent directions while the vascular system is being filled withcontrast medium.

The method implements, in general form, the steps that can be executedwith a device of the above-described type. For the explanation ofdetails, advantages and variants of the method, reference is thereforemade to the above description.

In particular, the projection pictures can be produced in the methodwith the aid of X-rays. In order to limit the radiation exposure for thepatient to a minimum during this process, the picture-taking rate and/orthe radiation dose is reduced to a necessary level during step b)compared with the conditions in step a).

Furthermore, projection pictures are preferably produced again from afixed direction after the termination of step b) while the contrastmedium is draining from the vascular system. As a result of tracking thecontrast-medium drainage, a second observation is available that permitsan assessment of the flow conditions in the vascular system.

These and other aspects of the invention are apparent from and will beelucidated with reference to the embodiments described hereinafter.

In the drawings:

FIG. 1 shows diagrammatically the device according to the invention forthe three-dimensional reconstruction of the flow conditions in avascular system during the inflow of the contrast medium;

FIG. 2 shows the device of FIG. 1 during the rotation of the X-raydevice;

FIG. 3 shows the device of FIG. 1 during the drainage of the contrastmedium.

The system shown in the Figures is based on a medical application, butthe present invention is not limited thereto. Within the framework ofthe medical application, the flow conditions are to be observed andreconstructed three-dimensionally in a vascular system 3, for example,in the coronary vessels. For this purpose, the device comprises arotation X-ray unit 1 having an X-ray source 2 and an X-ray detector 4for producing two-dimensional projections of the vascular system 3 andalso an injection device 5 for injecting a contrast medium into thevascular system. The injection device 5 may comprise, in particular, apump and also a catheter leading into the vascular system. Furthermore,the device is coupled to a control unit 6 (for example, a workstation)that can control the X-ray unit 1 and evaluate pictures producedtherefrom. Finally, the system also comprises an ECG unit 7 that iscoupled to the control unit 6 in order to make possible a correlation ofthe picture-taking procedure with the heartbeat phase.

The device described makes it possible to record from a singlecontrast-medium injection or with a single contrast-medium bolus boththe flow conditions with time and to reconstruct the vascular systemspatially. In order to achieve this, the control unit 6 is equipped witha suitable program for activating the device 1 so that thepicture-taking procedure described in detail below can be executed.

In the first step shown in FIG. 1 of the picture-taking procedure,projection pictures of the vascular system 3 are produced from aconstant projection direction A at a high picture-taking rate oftypically 30-80 pictures per second, preferably approximately 50pictures per second. In this connection, at the beginning of thepicture-taking series, the contrast-medium injection is effected so thatthe inflow of the contrast medium into the vascular system can bereflected in a time-resolved manner in the pictures.

When the contrast medium fills the entire vascular system 3, the secondphase of the picture-taking procedure can be initiated manually by auser or automatically by the control unit 6 with a rotation of the X-raydevice 2, 4 around the vascular system 3. An automatic initiation maytake place, for example, by an image analysis of the projection picturesproduced from position A. Equally, the control unit 6 can determine by acoupling to the injection device 5 when a certain amount of contrastmedium has been injected or a certain time has elapsed since thebeginning of the injection in order then to initiate the rotation.During the rotation of the X-ray device, projection pictures areproduced from different directions B_(i) from which thethree-dimensional shape of the vascular tree can be reconstructed usingknown methods.

FIG. 3 shows an optional last step in which, after termination of therotation (FIG. 2), X-ray projections of the vascular system 3 are onceagain produced from a fixed projection direction C. In these pictures,the drainage of the contrast medium from the vascular system in atime-resolved manner can, in particular, be observed so that furtheritems of information are available for the flow reconstruction. Inaddition, this observation also makes it possible to calculate fromadditional parameters such as, for example, the times for which thecontrast medium remains in a portion of the vascular system.

The initial and the final positions of the rotation of the X-ray systemmust of course be suitably calibrated. Furthermore, it is possible todispense with the stationary picture-taking phase in accordance withFIG. 1 if suitable pictures for the time assessment of the flow areproduced at the end of the injection (FIG. 3).

1. A device for the three-dimensional reconstruction of the flowconditions in a vascular system (3) with the aid of two-dimensionalprojections of the vascular system during a contrast-medium injection,comprising an imaging device (1) for producing two-dimensionalprojection pictures of the vascular system (3) taken from differentdirections (A, B_(i), C); an injection device (5) for the controlledinjection of a contrast medium into the vascular system (3); a controlunit (6) that is coupled to the imaging device (1) and that is designedto drive the imaging device in accordance with the following steps: a)production of projection pictures taken from the same projectiondirection (A) at a high picture-taking rate during the inflow of thecontrast medium after a contrast-medium injection; b) rotation of theimaging device around the vascular system (3) and production ofprojection pictures taken from different directions (B_(i)) while thevascular system (3) is filled with contrast medium.
 2. A device asclaimed in claim 1, characterized in that the imaging device is arotation X-ray unit (1, 2, 4).
 3. A device as claimed in claim 1,characterized in that, during the rotation of the rotation X-ray unit(1, 2, 4), the projection pictures are produced at a lowerpicture-taking rate and/or at a lower radiation dose.
 4. A device asclaimed in claim 1, characterized in that the control unit (6) isdesigned to drive the imaging device (1) after completion of therotation to produce projection pictures taken from a fixed projectiondirection (C) at a preferably higher picture-taking rate.
 5. A device asclaimed in claim 1, characterized in that the control unit (6) isdesigned to initiate the beginning of the rotation as a function of animage analysis of the projection pictures produced during the inflow ofthe contrast medium.
 6. A device as claimed in claim 1, characterized inthat the control unit (6) is coupled to the injection device (5) inorder to record and/or to control the injection process.
 7. A method forthe three-dimensional reconstruction of the flow conditions in avascular system with the aid of two-dimensional projections of thevascular system during a contrast-medium injection, comprising thefollowing steps: a) production of projection pictures taken from thesame projection direction (A) at a high picture-taking rate during theinflow of the contrast medium; b) production of projection pictures ofthe vascular system (3) taken from different directions (B_(i)) while itis filled with contrast medium.
 8. A method as claimed in claim 7,characterized in that the projection pictures are produced by means ofX-rays.
 9. A method as claimed in claim 8, characterized in that thepicture-taking rate and/or the radiation dose is reduced during step b).10. A method as claimed in claim 7, characterized in that, after stepb), projection pictures are produced from a fixed direction (C) duringthe drainage of the contrast medium from the vascular system (3).